This invention relates to a system for controlling an internal combustion engine and, more particularly, to a microprocessor-based electronic engine control system responsive to one or more sensed engine operating parameters for controlling one or more of such engine operating functions as, for example, fuel injection, ignition timing, EGR control, and the like.
Many of engine operating functions such as fuel injection, ignition timing, EGR control, and the like have been controlled based on engine load. A true indication of engine load may be obtained by the measurement of both engine speed and output torque, but a satisfactory sensor for measuring engine output torque is not available at this time. Because of this, it is the common practice to employ a single load sensor which provides an inference of engine load be sensing the absolute pressure within the engine intake manifold, the flow of air to the engine, or the angular position of the throttle valve. With engine control systems employing a single load sensor, however, a failure in such a load sensor will leads to a failure to perform proper engine operating function control, causing engine troubles.
The present invention provides an improved engine control system employing first and second load sensors which provide an inference of engine load by measuring first and second engine operating parameters. The system controls one or more engine operating functions based normally on the measurement of the first engine operating parameter but based on the measurement of the second engine operating parameter when the first engine operating parameter varies out of a predetermined range.